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Download Friction Types of Friction Frictional Forces Question: Friction and Wear
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Question: Friction You are in a tremendous hurry and you want your car to accelerate as quickly as possible when the light turns green. Tire damage is not an issue. Will you accelerate faster if you “burn rubber” (skid your wheels) or if you just barely avoid skidding your wheels? • Opposes the relative motion of two surfaces • Acts to bring two surfaces to one velocity • Consists of a matched pair of forces: – Object one pushes on object two – Object two pushes on object one – Forces have equal magnitudes, opposite directions • Comes in two types: static and sliding Types of Friction Frictional Forces • Static Friction • Increase when you: – Acts to prevent objects from starting to slide – Forces can vary from zero to an upper limit • Sliding Friction – Acts to stop objects that are already sliding – Forces have fixed magnitudes – push the surfaces more tightly together – roughen the surfaces • Peak static force is greater than sliding force – Surface features can interpenetrate better – Friction force drops when sliding begins Question: Friction and Wear You are in a tremendous hurry and you want your car to accelerate as quickly as possible when the light turns green. Tire damage is not an issue. Will you accelerate faster if you “burn rubber” (skid your wheels) or if you just barely avoid skidding your wheels? • Static friction – No work is done (no distance) – No wear occurs • Sliding friction – Work is done (distance in the direction of force) – Wear occurs – Work is turned into thermal energy •1 Conserved Quantity Forms of Energy • Energy • Kinetic – energy of motion • Potential – energy stored in forces between objects – A directionless (scalar) quantity – Can’t be created or destroyed – Transferable between objects via work – Can be converted from one form to another – – – – – – – Gravitational Elastic Magnetic Electric Electrochemical Chemical Nuclear Types of Energy Rollers • Ordered Energy • Eliminate sliding friction at roadway • Are inconvenient because they keep popping out from under the object – Organized in chunks – Example: Work • Disordered Energy – Fragmented – Example: Thermal energy • Sliding friction disorders energy – Converts work into thermal energy Wheels Bearings • Eliminate sliding friction at roadway • Are convenient because they don’t pop out • Wheel hubs still have sliding friction • Eliminate sliding friction in wheel hub • Behave like automatically recycling rollers •2
